The invention is directed to the field of data processing and more particularly to memory devices for use in and with data processing equipment. Memory devices may be broken down into two types by their storage characteristics, namely, stable (non-volitile) or volitile. A stable storage device is one which retains its data until the device is erased or written over and is uneffected by the presence or absence of system operating or maintenance voltages. For example, a magnetic drum memory stores data by the recording at discrete spots on the surface of the drum. The drum retains such a recording regardless of the rotation or non-rotation of the drum and the presence or absence of power to the associated data processor.
A volitile storage device is one which retains its storage state only so long as the device is operational. For example, if transistor flip-flops are used as the storage device they will retain their storage condition only so long as the required operating voltages are applied. In the event of a power failure, the removal of operating voltages would destroy the stored value since the resumption of the correct storage state could not be assured when the power was restored.